Create a way to pip install just the client + dependencies

As someone who wants to use the client to heliotrapi when I do `pip install heliotrapi` I get a lot of dependencies that I don't really need, e.g. `pyqt` from `xrpd-toolbox`. This bloats my python env and leads to potential clashes like https://github.com/DiamondLightSource/crystallography-bluesky/pull/62#pullrequestreview-4426326414.

## Acceptance Criteria
- I can run `pip install heliotrapi[client]` and just get the things I need for the client